Winter storage: Getting your engine all (oil) fogged up

If only all automotive maintenance projects were supposed to end in a cloud of smoke. Though somewhat hard to believe, that's the intention when "fogging" an engine before long-term storage.

The Problem: Moisture

When an engine sits inactive over the winter, the sensitive parts inside get cold and attract whatever moisture is in the air. This can lead to corrosion on cylinder walls, pistons, rings, and valves. Once the engine is started again, plenty of bad stuff can result: scoring of cylinder walls, wear on the rings, and even a stuck valve. Fogging oil wraps the internals in a nice blanket of oily goodness as a preventative measure. Although major wear and broken parts are unlikely over just one winter, fogging oil is cheap insurance for the parts you can't easily see.

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Fogging Oil

Zach Bowman

The don'ts of fogging

Fogging isn't recommended for all engines, so let's get some warnings and caveats out of the way first. It shouldn't be used on a diesel, as the oil can ignite and cause a runaway condition. It's also not recommended for direct-injection motors, which includes basically anything sold new today. Some products are safe for catalytic converters and other emissions equipment, while others aren't; read the label and look for one that explicitly states it to be sure. If the engine is equipped with a mass-airflow sensor, be sure the oil is added downstream of it. Any gas engine with a carburetor—be it in a car, motorcycle, or lawn tractor—is cleared for fogging.

How to fog

Most fogging oil comes in a spray can, and application is pretty simple. Tear down what you need to for access to the throttle body (or bodies), and then spray the contents in while the engine's running. In short order, oily smoke (that would be the fog) should start flowing from the exhaust. Shut the engine down—fogging complete.

For added protection, you can pull each spark plug and spray another dose of oil into each cylinder after the foggy part. In a modern engine, with its plastic covers and shoehorned packaging, this can range from "minor pain" to "impossible without major disassembly." Same goes for some older stuff as well. It's a cinch with motorcycles and lawn equipment, but you might skip it on your LT1 Camaro. There's also a fog-free method, in which you skip the whole-engine protection of adding the oil upstream and simply squirt each cylinder. Less dramatic, and it can hardly be called fogging.

Marvel Mystery Oil

Zach Bowman

Alternatives

Other products, such as Marvel Mystery Oil, come in a bottle; the liquid can either be added in the fuel mixture or glugged straight into the throttle body. You get the same fog and protection, just in a different initial form. Some of these bottled products—Marvel Mystery Oil again—also claim to work as a fuel stabilizer, so you can potentially kill two birds with one stone.

If you're still unsure, or you have a newer engine with delicate sensors you'd rather not risk, the other option is starting the engine periodically over the winter. This involves getting the engine up to temperature to burn off any water that has condensed in the engine, as well as in the exhaust and oil pan. Starting the engine and shutting it down before reaching operating temp will do more harm than good. It goes without saying, but we're going to say it anyway, that this should be done with the garage door open. It's best to avoid fogging your own lungs.